<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
    </style>
</head>

<body>
    <button>按钮1</button>
    <button>按钮2</button>
    <button>按钮3</button>
    <button>按钮4</button>
    <button>按钮5</button>

    <script>

        //获取所有按钮
        var btns = document.getElementsByTagName('button')
        //btns 得到的是伪数组 里面的每一个元素 btns[i]
        for (var i = 0; i < btns.length; i++) {
            btns[i].onclick = function () {

                //1.我们先把所有的按钮背景颜色去掉
                for (var i = 0; i < btns.length; i++) {
                    btns[i].style.backgroundColor = '';
                }

                //2.然后才让当前的背景颜色变为pink
                this.style.backgroundColor = 'pink';
            }
        }
    </script>
</body>

</html>